Reactor for chemical conversion of a feedstock with heat inputs and feedstock/catalyst cross-circulation

ABSTRACT

A chemical conversion reactor contains a substantially vertical catalytic bed between an upper end and a lower end and comprises, in combination: close to its upper end, at least one means for introducing a solid catalyst, means for introducing and evacuating said feed allowing its flow in a substantially horizontal direction through the catalytic bed, means for heating said feed integrated into said reactor, said reactor comprising, close to its lower end, at least one means for extraction of the catalyst, which extraction is differentiated between an upstream portion and a downstream portion of said catalytic bed, with respect to the direction of flow of said feed.

[0001] The chemical, petroleum and petrochemical industries employ manyendothermic chemical reactions, for example cracking reactions,dehydrogenation reactions or hydrocarbon reforming reactions.

[0002] Certain of those reactions are reversible and limited by athermodynamic equilibrium. In that case, the cooling occurring in thecatalytic bed due to the endothermic nature of the reaction limits thereactant conversion.

[0003] One method for obtaining a high conversion consists ofintroducing heating surfaces into the catalytic bed, or using aplurality of catalytic beds separated by zones for re-heating thereaction fluid.

[0004] In many cases, in particular for hydrocarbon dehydrogenation, thecatalyst is at least partially deactivated during the reaction, forexample by coking, and must be extracted, continuously or at distincttime intervals, and replaced by new or regenerated catalyst.

[0005] Processes such as catalytic hydrocarbon reforming are known inwhich the reaction feed successively traverses a plurality of catalyticbed reactors, with intermediate re-heating between the reactors tocompensate for cooling of the reaction fluid due to the endothermicnature of the reaction. The catalyst moves from one reactor to another,as a co-current or as a counter-current to the feed before beingregenerated and recycled. The catalyst is used efficiently andhomogeneously coked before being regenerated.

[0006] A first aim of the invention is to provide a reactor for carryingout a chemical conversion process in catalytic beds with means forsupplying heat integrated into said reactor, and thus with a verycompact reaction zone, combined with efficient use of the catalyst. Afurther aim of the invention is to provide a process for converting afeed (usually a hydrocarbon feed) undergoing an endothermic reactionusing said reactor. The scope of the present invention also encompassesusing a series of reactors at least one of which is in accordance withthe present invention.

[0007] To this end, the invention concerns a reactor for chemicalconversion of a feed, said chemical conversion reactor containing asubstantially vertical catalytic bed between an upper end and a lowerend, and comprising in combination:

[0008] close to its upper end, at least one means for introducing asolid catalyst;

[0009] means for introducing and evacuating said feed allowing its flowin a substantially horizontal direction through the catalytic bed;

[0010] means for heating said feed integrated into said reactor;

[0011] in which said reactor comprises, close to its lower end, at leastone means for extraction of the catalyst, which extraction isdifferentiated between an upstream portion and a downstream portion ofsaid catalytic bed, with respect to the direction of flow of said feed.

[0012] The reactor can be a reactor-exchanger with heating surfacesimmersed in the catalytic bed; it can also comprise a plurality ofcatalytic beds separated by non-catalytic zones for heating the reactionfeed. In each of these zones, the reaction feed traverses a heatexchanger, supplied with a heat transfer fluid.

[0013] Heat transfer fluids that can be used include pressurised steam,for example between 0.5 MPa and 1.20 MPa, preferably between 0.6 MP and1 MPa absolute, limits included, hydrogen or a hydrogen-containing gassuch as a hydrogen-rich recycle gas, such as that used in certainprocesses to dilute the reaction feed to protect the catalyst. It isalso possible to use the unconverted feed itself, or liquids such asmolten salts or liquid sodium.

[0014] The differentiated catalyst extraction means is normally selectedfrom the group formed by continuous and discontinuous extraction means.

[0015] Preferably, the catalytic bed comprises a plurality of catalyticzones separated by noncatalytic zones for heating the feed.

[0016] In a preferred feature of the invention, the most upstreamcatalyst extraction means differs from at least one downstreamextraction means, and particularly that located the furthest downstream,in its lower extraction capacity (the concepts of upstream anddownstream being with respect to the direction of flow of the feed).

[0017] The invention also proposes a process for chemical conversion ofa feed using a reactor as described above.

[0018] Typically, the feed is a hydrocarbon feed, often with an addeddiluent (for example steam, hydrogen, nitrogen or a mixture of thesegases).

[0019] In a particular implementation of the invention, the chemicalconversion process is a process for catalytic dehydrogenation of aparaffinic hydrocarbon feed.

[0020] We shall now refer to FIG. 1, which is a non-limitingrepresentation of a reactor R in accordance with the invention used tocarry out an endothermic reaction.

[0021] The reaction feed is introduced into reactor R via a line 1; ittraverses, in succession, a catalytic bed 3 a, then a heat exchanger 4a, then a second catalytic bed 3 b, then a second heat exchanger 4 b,then a third and last catalytic bed 3 c, before leaving the reactor viaa line 2. The catalyst is introduced into the reactor at the headthereof via a line 9. It is distributed into the three catalytic beds 3a, 3 b, 3 c in which they flow under gravity in downflow mode. Eachcatalytic bed has a separate hopper for evacuating the catalyst: 7 a forbed 3 a, 7 b for bed 3 b and 7 c for bed 3 c.

[0022] Extraction valves 8 a, 8 b, 8 c at the bottom of each of thecatalytic beds can separately extract used catalyst flowing in each ofthe catalytic beds in series. The catalyst is evacuated via lines 80 a,80 b and 80 c.

[0023] Heat exchangers 4 a and 4 b are fed by heat transfer fluidintroduced via lines 5, 5 a and 5 b, this fluid leaving the exchangervia lines 6 a, 6 b and 6.

[0024] At the upper portion of beds 3 a and 3 b, a substantially inertgas is introduced via lines 10, 10 a and 10 b. The function of the gasis to provide a barrier gas to prevent feed passing from bed 3 a to bed3 b and by-passing exchanger 4 a, and similarly preventing feed passingfrom bed 3 b to bed 3 c and by-passing exchanger 4 b.

[0025] Typically, this gas can be a diluent for the fed, for examplesteam or a hydrogen-rich recycle gas.

[0026] The unit functions as follows.

[0027] The feed, pre-heated to the reaction temperature, traverses thethree catalytic beds (or zones) 3 a, 3 b, 3 c in series, with twointermediate re-heating steps.

[0028] The catalyst, introduced via line 9, is extracted continuously ordiscontinuously via lines 80 a, 80 b, 80 c.

[0029] In the reactor, in accordance with the invention, the catalystflowing in bed 3 c is preferably renewed more rapidly than that in bed 3a. Typically, the catalyst ages more rapidly and deactivates and cokesmore rapidly at the end of the reaction zone, i.e., in the downstreambed 3 c more than in the upstream bed 3 a. Preferably, 3 c is renewedmore rapidly than 3 b, which is itself renewed more rapidly than bed 3a.

[0030] The invention thus enables the catalyst to be used efficiently,which catalyst is extracted in a relatively constant state ofdeactivation.

[0031] When operation is continuous, valves 8 a, 8 b, 8 c can be used toadjust the differentiated catalyst extraction.

[0032] When operation is discontinuous, varying quantities of catalystcan be extracted at intervals depending on the catalytic zones (higherextraction rates in the downstream zones in the direction of feed flow).

[0033] It is also possible to carry out more frequent catalystextraction in the downstream zone 3 c than in zone 3 b and/or in zone 3b than in zone 3 a. It is also possible to modulate the frequency andquantities of catalyst extracted.

[0034] Finally, it is possible to carry out limited extraction of theused catalyst (for example 10% to 33% by volume of each bed) or to renewthe entire volume of an individual bed (or zone): 3 a, 3 b or 3 c. Inthis case, the catalyst in zone 3 c is preferably renewed morefrequently than that in zone 3 a.

[0035] The reactors of the invention can contain 2 to about 20 catalyticzones separated by heat exchange zones.

[0036] The reaction fluid can also be introduced laterally and flowhorizontally, as a crosswise current with the feed.

[0037] It is possible to use thin beds, for example 5 to 10 cm thick, orof medium thickness, for example between 10 and 80 cm, and if theprocess demands it, low or high space velocities (for example 10 to 250h⁻¹). The temperatures depend on the process but are frequently in therange 250° C. to 950° C., preferably between about 400° C. and about700° C. These values do not limit the invention.

[0038] The scope of the invention also encompasses the case whereinthere is but a single catalytic bed, or beds in parallel, with acrosswise feed/catalyst flow.

[0039] The reactor of the invention can carry out chemical conversion ofa feed in the presence of a catalyst while providing each of thecatalytic zones with the necessary amount of heat. It also enables theat least partially deactivated catalyst to be extracted in adifferentiated manner.

[0040] The reactor of the invention can maintain a high catalyticactivity and/or productivity for the desired product.

[0041] The invention can in particular be employed for hydrocarbonreforming, for dehydrogenating ethylbenzene, and for dehydrogenatingparaffins such as propane, n-butane, isobutane, primarily linearparaffins containing 10 to 14 carbon atoms, and for the production ofolefins for the production of alkylbenzenes, or for other chemicalreactions.

1. A chemical conversion reactor, containing a substantially verticalcatalytic bed between an upper end and a lower end, and comprising incombination: close to the upper end of said reactor, at least one meansfor introducing a solid catalyst; means for introducing and evacuatingsaid feed allowing its flow in a substantially horizontal directionthrough the catalytic bed; means for heating said feed integrated intosaid reactor; characterised in that said reactor comprises, close to itslower end, at least one means for extraction of the catalyst, whichextraction is differentiated between an upstream portion and adownstream portion of said catalytic bed, with respect to the directionof flow of said feed.
 2. A reactor according to claim 1, in which themeans for differentiated catalyst extraction is selected from the groupformed by continuous and discontinuous extraction means
 3. A reactoraccording to claim 1 or claim 2, in which the catalytic bed comprises aplurality of catalytic zones separated by non-catalytic zones forheating the feed.
 4. A reactor according to any one of claims 1 to 3, inwhich the most upstream catalyst extraction means differs from the mostdownstream extraction means in its lower extraction capacity.
 5. Aprocess for chemical conversion of a feed using a reactor according toany one of claims 1 to
 4. 6. A chemical conversion process according toclaim 5, in which the feed is a hydrocarbon feed.
 7. A chemicalconversion process according to claim 5 or claim 6, in which catalyticdehydrogenation of a paraffinic hydrocarbon feed is carried out.